Air filter



FIG. 1 is a top and front perspective view of an air filter showing my new design;

FIG. 2 is a rear elevation view thereof;

FIG. 3 is a front elevation view thereof;

FIG. 4 is a right side elevation view thereof;

FIG. 5 is a left side elevation view thereof;

FIG. 6 is a bottom plan view thereof; and,

FIG. 7 is a top plan view thereof. 

The ornamental design for an air filter, as shown and described. 